1. Field of the Invention
The present invention relates to an internal combustion engine provided with a combustion heater for elevating a temperature of an engine related element such as cooling water or intake air.
2. Description of the Related Art
In an internal combustion engine to be mounted on an automotive vehicle or the like, in particular, an internal combustion engine such as a diesel engine in which a heat quantity is likely to be small, a technique to additionally provide a combustion heater for the purpose of acceleration of warming up the internal combustion engine or enhancement of a passenger room heating device in a cold state.
The above-described combustion heater is provided with a combustion chamber which is independent of the internal combustion engine. Furthermore, the combustion heater is provided with a heat exchange portion composed of a water path formed so as to surround the combustion chamber.
The water path (water path in the heater) of the above-described heat exchanger and a cooling path of the internal combustion engine are in communication with each other through a cooling water leading path for introducing the cooling water from the cooling path of the internal combustion engine to the water path in the heater and a cooling water discharge passage for introducing the cooling water from the water path in the heater to the cooling path of the internal combustion engine. A heater core of the passenger room heating device is provided in the midway of the cooling water discharge passage.
In the thus constructed combustion heater, a part of fuel of the internal combustion engine is burnt in the combustion chamber in a cold state or the like of the internal combustion engine, and at the same time, the cooling water for the internal combustion engine is introduced to the water path in the heater through the cooling water leading path.
In this case, the heat generated as a result of the combustion within the combustion chamber is transferred to the cooling water in the heat exchanger portion to elevate the temperature of the cooling water. The cooling water (hot water) which has been heated in the heat exchange portion is discharged from the water path in the heater to the cooling water discharge passage to be returned back to the cooling water path through the heater core. When the above-described hot water has passed through the heater core, a part of heat of the hot water is transferred to the heating air that flows through the heater core, thereby the temperature of the heating air being elevated.
According to the above-described combustion heater, it is possible to elevate the temperature of the heating air or the engine cooling water in an earlier stage in the cooling operation of the internal combustion engine and it is possible to enhance the acceleration of the warmup of the engine and the heating capacity.
However, in the combustion heater, since the combustion is conducted by utilizing the part of the fuel for the internal combustion engine, there are cases where the burnt gas emitted from the combustion heater contains harmful gas components like the emission of the internal combustion engine. In those cases, it is necessary to discharge the emission after purifying the harmful gas components contained in the burnt gas.
In order to meet such a requirement, Japanese Patent Application Laid-Open No. Sho 60-78819 describes "HEATING DEVICE FOR A VEHICLE PROVIDED WITH A COMBUSTION HEATER". In the heating device disclosed in this publication, an exhaust port of a heater exhaust pipe for discharging the gas burnt in the combustion heater is provided upstream of the exhaust gas purifying device of the exhaust pipe of the internal combustion engine, and the burnt gas to be discharged from the combustion heater is introduced into the exhaust gas purifying device for the internal combustion engine to thereby purify the harmful gas components contained in the burnt gas with the exhaust gas purifying device for the internal combustion engine.
It is possible to exemplify a three-element catalyst, an adsorption reduction type lean NOx catalyst, a selective reduction type lean NOx catalyst or the like for the exhaust gas purifying device of the internal combustion engine. However, since these exhaust gas purifying devices are activated so that the harmful gas components contained in the exhaust gas may be purified when the catalyst bed temperature exceeds a predetermined level, in order to positively purify the burnt gas from the combustion heater and the exhaust gas from the internal combustion engine, it is necessary to keep the exhaust gas purifying devices at the activation temperature or more.
However, in the case where the internal combustion engine is a diesel engine, a heat generation amount of the internal combustion engine tends to be small in a low load operational region, and the exhaust gas temperature is likely to be low. Accordingly, it is difficult to keep the exhaust gas purifying device at the activation temperature or more only by the exhaust gas of the internal combustion engine.
In contrast, as in Japanese Patent Application Laid-Open No. Sho 60-78819 entitled "HEATING DEVICE FOR A VEHICLE PROVIDED WITH A COMBUSTION HEATER", it is possible to propose that the burnt gas that is relatively high in temperature from the combustion heater is introduced into the exhaust gas purifying device to thereby elevate the temperature of the exhaust gas purifying device. However, since the temperature of the exhaust gas to be discharged from the above-described combustion heater is lowered by the heat exchange with the heating air in the heat exchange portion, there is a problem in that it takes long time to elevate the temperature of the exhaust gas purifying device up to the activation temperature, and the exhaust emission would become worse in the meantime.